Colour replacement not working properly

Good morning Aman!

The Replace Color funtion is based on selecting an area by color, which should make it easier to select an area. But, your shapes have a different color border on each one--that is why Replace color did not select the edge. I would suggest making your selection using Color Range because it gives you the option of making a selection that you can then change.

First, Select Color Range from the Select menu and a color. Note the settings I have here in the image below. Click Ok and you will have a selecion of that color, but notice in the 2nd image below that it didn't select the border around the shape--the same as Replace Color? 

#2 Save your Selection—Choose Save Selection from the Select Menu and name it what ever color you chose.

#3 Do this with all three colors so that you have a selection saved for each one.

#4 From the Select Menu, choose Modify>Expand and dependng on the resolution of your image, input a number that expands the selection to include the border area. See the image below:

Then I would also suggest using Select>Modify>Smooth to Smooth out your selection, and again the value you put in there will be different depending on what your resolution is. The image above is a screenshot so it is 72 ppi and it might be different with your orgiinal image.

Once you have followed those steps, you can select a color and fill each shape to get the effect you want

Let us know if that helps or if you still have any questions.

Michelle